As wireless communications devices become increasingly ubiquitous, support of multiple communications protocols is often required. As a result, many wireless communications devices are multi-mode devices, which are capable of operating using two or more RF communications bands, which may have frequency ranges that are widely separated from one another, are capable of operating in a half-duplex or a full-duplex operating mode, may operate over a wide range of output power levels, may use multiple modulation techniques, or any combination thereof. To enable high levels of integration, the wireless communications devices may need to be physically small. Therefore, sharing as many components as possible when operating in different modes is desirable. For example, use of a common power amplifier, a common antenna, or both may be desirable to reduce size, cost, or both. However, one or more adaptive RF impedance translation circuits may be needed to properly interface a common power amplifier to an RF antenna over all operating conditions.
One or more adaptive RF impedance translation circuits may be needed to properly interface an RF antenna to receive circuitry, to a common power amplifier, or the like over all operating conditions. Specifically, in a portable wireless communications device, an RF antenna may undergo large loading changes that are dependent upon nearby physical conditions, such as proximity to a user's body, proximity to metallic objects, or the like. Such loading changes may cause large changes in a voltage standing wave ratio (VSWR) associated with large impedance changes of the RF antenna. By coupling an adaptive RF impedance translation circuit to the RF antenna it may be possible to compensate for VSWR changes and present an impedance to other circuitry that has reduced impedance fluctuations. Additionally, portable wireless communications devices are often battery powered. To conserve power, any adaptive RF impedance translation circuits may need low insertion loss to reduce power consumption.
Thus, there is a need for an adaptive RF impedance translation circuit that can operate over at least two communications bands having frequency ranges that are widely separated from one another, has low insertion loss, is physically small, can operate efficiently over a wide power range, and has a wide impedance adjustment range.